1. Technical Field
The present disclosure generally relates to downhole tools and in particular to methods and apparatus for collecting a downhole sample.
2. Background Information
Oil and gas wells have been drilled at depths ranging from a few hundred feet to as deep as 5 miles. Wireline and drilling tools often incorporate various sensors, instruments and control devices in order to carry out any number of downhole operations. These operations may include formation testing and monitoring and tool monitoring and control.
Formation testing tools have been used for monitoring formation pressures along well boreholes, obtaining formation fluid samples, and predicting performance of reservoirs. Such formation testing tools typically contain an elongated body having an elastomeric packer and/or pad that is sealingly pressed against a zone of interest in the borehole to collect formation fluid samples in fluid receiving chambers placed in the tool.
Often the fluid receiving chambers become contaminated with drilling mud, formation fluids from prior sampling, water, and other contaminants. There is also difficulty encountered in measuring samples to accurately estimate a downhole fluid property. For example, downhole fluids can be unstable and/or the downhole tools can provide inaccurate results. There is a need, therefore, for improved apparatus and methods for reducing the potential for drilling fluid and other impurities from contaminating downhole sample chambers and/or acquiring more accurate estimations of one or more downhole fluid properties.